1. Field of the Invention
The present invention relates to a security system and a monitoring method, and particularly relates to a security system and a monitoring method that use a power line communication technology utilizing a power line to provide data communication.
2. Description of the Background Art
A Power Line Communication (PLC) technology, which can utilize an existing power line to provide data communication, superimposes a data signal with a high frequency (e.g. 10-450 kHz) on a power carrier wave (50-60 Hz) on a power line of a commercial power supply, to provide data communication. If a frequency band allocated to the data signal is extended to further enhance the speed of data communication, connectivity to the Internet can also be provided by the use of a power line. The use of the power line communication technology has such an advantage as to allow data communication from any room as long as a power receptacle is installed therein, eliminate the need of work for installing new wiring, and thereby achieve high versatility.
In recent years, even in ordinary households, there has been a growing interest in a crime prevention security system. For example, Japanese Patent Laying-Open No. 2003-023678 discloses a monitoring control device capable of easily monitoring the state of a building from a remote site. According to the disclosure, the device is provided with at least one sensor installed in a prescribed place of the building for detecting the internal state of the building, data conversion means for converting an output signal of the sensor into digital data, a personal computer reading the digital data to store the read data, data transmission means for transmitting through the Internet the digital data stored in the personal computer, and a storage server receiving the digital data transmitted by the data transmission means to store the digital data as security information.
However, it is necessary to connect the personal computer installed inside the building to the Internet, resulting in low versatility. Therefore, there have been proposed some security systems that use a power line communication technology and achieve high versatility.
For example, Japanese Patent Laying-Open No. 2003-331371 discloses a self-security system that implements unattended reception in the case of an unexpected visitor, and establishes security while all the people are away, in a state of absence of the people. According to the disclosure above, the system is provided with security monitoring means for receiving through a power line network an ID specific to a sensor and obtained from the sensor, the sensor being attached to a place that requires security, and self-security service provider means for grasping the state based on the correspondence between the sensor-specific ID registered in advance and the place where the sensor is attached, and providing the grasped state to a cellular telephone terminal through electrical mail transmission.
Japanese Patent Laying-Open No. 2002-373389 discloses a security system that is capable of operating itself when an abnormal event occurs, eliminates the need of work for installing a private line, and enjoys high degree of flexibility in installation. According to the disclosure above, the security system uses a power line as communication media to distribute monitored information such as video information or audio information from a transmission device to a receiving device, so as to monitor the presence or absence of an abnormal state. In this system, an abnormal event sensing portion, which is formed of a temperature sensor portion, an audio sensor portion or others, senses whether or not an abnormal event occurs in surroundings.
Japanese Patent Laying-Open No. 2002-183845 discloses a high-functionality crime prevention device that has a crime prevention function and an evidence acquisition function with a simple configuration, and is suitable for being used in an ordinary private house, a small-sized office and others. According to the disclosure above, the system senses an illegal intruder recorded by a home video recorder, causes an alarm to generate an alert, and sends a notification of illegal intrusion to a terminal on a remote center side through a public network.
There has conventionally been proposed a security system that uses a power line communication technology and has high versatility, and hence there is demanded an implementation of a crime prevention security system that is less likely to be noticed by an intruder and has high versatility.